The present invention relates generally to antenna systems. More specifically, the present invention relates to a cavity-driven antenna system having a passive antenna element.
The purpose of an antenna system is to radiate efficiently the power supplied to it in the form of an electromagnetic wave. Some of the simplest known antenna systems include a single antenna element which is driven with a current to transmit an electromagnetic wave at the wavelength of the applied current. Known antenna elements include, for example, a dipole, a quarter-wave monopole, a helix, a spiral and a loop.
Antenna systems may also be required to concentrate the radiated power (i.e., the propagated electromagnetic wave) in a given direction and to minimize the radiated power in other directions. To achieve such directionality often requires a complicated antenna system that incorporates a number of individual antenna elements (e.g., an array configuration) and/or the addition of a reflector or cavity. For example, an antenna system comprising a helix antenna element within a relatively long, extended cavity has better directionality than a helix antenna alone because the cavity can suppress the side-lobes (i.e., off-axis radiated power normally present in an antenna pattern) normally present with a helix antenna alone.
FIG. 1 illustrates a cross-section view of a known antenna system having a helix antenna element within an extended cavity. The antenna system 10 has an antenna element 11 disposed within a cavity 12. The antenna element 11 is driven by a current from a power source 13. The cavity has an extended length to provide additional directivity; the length of the cavity is extended in the sense that it is typically longer than several wavelengths of the antenna system. The extended length of the cavity suppresses the propagation of side-lobes in the antenna pattern.
Although known antenna systems can provide some level of directionality, such systems suffer several shortcomings. For example, the use of an extended cavity adds to the weight, size and cost associated with the antenna system. Antenna systems that use multiple antenna elements, for example, in an array configuration again add to the cost and complexity associated with the antenna system.